1. Field of the Invention
The present invention relates generally to a cellular mobile communication system. In particular, the application relates to an apparatus and method for measuring and reporting uplink load in a base station (BS).
2. Description of the Related Art
Radio channel resources are occupied during a call connection between a mobile station (MS) and a BS in a mobile communication system. While a wired system provides a dedicated line to a terminal irrespective of whether the dedicated line is now used or not, a wireless system cannot allocate a new call or increase the rate of an on-going call for an MS if all available radio resources of a BS are in use. Allocating a new call or increasing the rate of an on-going call beyond available radio resources seriously affects all MSs communicating with the BS and its adjacent BSs. Therefore, the system manages radio resources by rapidly disconnecting the call or reducing the data rate, and monitoring the radio resources. Aside from call allocation and rate increase, factors such as fading may change the amount of available radio resources. Therefore, it is very important in radio communication technology to detect the status of radio resources and to take a corresponding action.
2nd generation (2G) mobile communication systems focus on voice service. The voice service is provided via a relatively slow traffic channel on both the downlink and the uplink. The downlink refers to a direction from a BS to an MS and the uplink refers to a direction from an MS to a BS. Due to increasing user demands for more services beyond the simple voice service, 3rd generation (3G) systems have been developed to additionally provide high-speed data service and international standards have been established for the 3G systems. These 3G systems comprise Code Division Multiple Access 2000 1× (CDMA 2000 1×), 1×Evolution in Data Only (1×EV-DO), 1×Evolution in Data and Voice (1×EV-DV), and Wideband CDMA (WCDMA).
Studies of the uplink in the 3G systems have been voice-oriented. They have been made on call approval control and sector capacity analysis in relation to voice call. As high-speed data service has recently been added to the basic voice service on the uplink, many challenging issues have emerged. First of all, accurately evaluating the current radio resources status, that is, the current load is an increasingly significant concern so as to determine an optimum data rate for a high-speed data service as much as possible without impairing the quality of existing calls, especially voice calls.
In the mobile communication system, sector resources are limited by interference from other sector as well as from users within the same sector. A load-based uplink load measuring method was proposed but this method is limited to measuring only the load from users within the same sector. To solve the problem, a Rise Over Thermal (ROT)-based method has been addressed which reflects load comprising interference and to implement this method, efficient ROT measurement has become an issue. ROT is defined asROT[dB]=total reception power[dBm]−(thermal noise power+external power)[dBm]).  (1)
The basic issue of ROT measurement is to measure thermal power and external interference power. Although the total reception power can be measured all the time irrespective of the presence or absence of call, the sum of the thermal power and the external interference power (hereinafter, referred to as background power) can be measured only where no call is placed in the BS and the adjacent BSs.
The CDMA2000 EV-DO system defines a silence period to measure the background power. All MSs discontinue transmissions for the silence period, and the reception power measured for the silence period is the background power. However, other systems than CDMA2000 EV-DO, such as CDMA2000 1×, EV-DV, and WCDMA, do not provide the silence period, that is, the period for which MSs stop their on-going communications. It is not easy to control uplink load by ROT measurement in such systems.
Compared to the CDMA system where a BS itself controls uplink load, a base station controller (BSC) is responsible for control of uplink load and thus a ROT measured by a BS must be reported to the BSC in the WCDMA system. However, the standard interface between the BS and the BSC does not support a ROT field required for controlling the uplink load. It supports only a Received Total Wideband Power field by which the BS reports received power to the BSC. Accordingly, a need exists for a technique of accurately measuring ROT for controlling uplink load and interfacing the ROT measurement to a BSC in a mobile communication system like the WCDMA that does not provide a silence period.